How long will the Israelis wait before striking out at their sworn enemy?

Operation Opera went like clockwork. It took only 80 seconds for Saddam Hussein’s cherished ambition to build a nuclear weapon, over which his experts had laboured for six years, to be obliterated by Israeli strike aircraft swooping from a blazing summer sky.

The destruction of Iraq’s Osirak reactor on June 7, 1981 was among the most successful preventive attacks in modern history. Just 16 bombs dropped by eight F-16s derailed Saddam’s nuclear programme, buying enough time for the dictator to seal his own downfall by occupying Kuwait and paving the way for the invasion of 2003. The history of the Middle East changed – and not a single Israeli aircraft was lost.

With Operation Opera seared into their collective memory, is it any wonder that Israeli leaders look at Iran’s nuclear ambitions and contemplate the same solution? If the rhetoric coming from the defence ministry in Tel Aviv is to be believed, the option of destroying Iran’s nuclear facilities with a series of air strikes is being considered more seriously than ever before. Indeed some anonymous briefings to the Israeli media come close to suggesting that a decision to launch a new Operation Opera has already been taken, with timing the only remaining issue.

An unnamed “decision-maker” – presumed to be Ehud Barak, the defence minister – told the Haaretz newspaper that Israel could not afford to wait for the US to act. “We need to look at the reality right now with total clarity,” he said. “Israel is strong and Israel is responsible, and Israel will do what it has to do.”

If so, the three months before the US presidential election in November provide the obvious window for an Israeli strike. The impression given is that the world may be a few weeks away from another war. As for the possible consequences, Israel’s outgoing civil defence minister says that any conflict would take place “on a number of fronts”, lasting for 30 days and costing about 500 Israeli lives.

The phrase “a number of fronts” is significant. Unlike Saddam in 1981, Iran has numerous ways of hitting back. The big difference between Operation Opera and a strike on Iran today is the risk of retaliation. To begin with, Iran could respond directly, using its arsenal of Shahab-3 ballistic missiles, each capable of striking targets up to 1,200 miles away, with Israel comfortably within range.

Perhaps more dangerously, Iran could act through its armed allies. Over the years, Tehran has supplied Hizbollah, the radical Shia movement in south Lebanon, with up to 40,000 rockets, all of them trained on Israeli targets. The last time Hizbollah fired its weapons was during the war of 2006, when Israel’s northern port town of Haifa was the main civilian target.

Today, Hizbollah’s arsenal in Lebanon is believed to include more advanced rockets with longer ranges and heavier payloads, bringing Tel Aviv itself within reach. More than half of Israel’s population of 7 million would probably be within range of any new bombardment launched by Hizbollah.

Finally, Iran could try to impose some of the pain of an Israeli strike on the rest of the world. Some 35 per cent of the world’s seaborne oil shipments pass through the Strait of Hormuz on its southern coast. If Iran tried to block this channel, the oil price would probably rocket, dealing a grave blow to the world economy.

Guaranteeing failure, however, would require the sea power of the US Navy. And there lies the rub. Any war started by Israel would almost certainly drag in America at an early stage. Only an operation by the US Fifth Fleet, based in Bahrain, could guarantee free passage through the Strait of Hormuz.

The anonymous “decision-maker” who briefed Haaretz shied away from the probability of America becoming an unwilling belligerent, saying: “We will absolutely not deliberately drag the US into war. If we decide to undertake an operation, it must be an independent act that justifies itself without igniting some large chain reaction.”

But Iran gets to decide whether to ignite a “chain reaction” or not. Tehran might react to any Israeli strike by playing the victim, not hitting back, and seeking to rally international sympathy. Western diplomats point to a precedent from 1988, when a US warship shot down an Iranian airliner, killing 290 people, and Tehran refrained from lashing out.

If, however, Iran did opt to threaten the Strait of Hormuz, US involvement would probably be inevitable. The decision on whether to embroil the US will thus be taken in Tehran, not Tel Aviv.

America is well aware of this – and President Obama’s administration is doing its best to restrain its erstwhile ally. There remains a chance that Israel is bluffing. On the face of it, there would be a clear diplomatic rationale for issuing empty threats. In the past, every rattle of an Israeli sabre has led the US and Europe to impose tighter sanctions on Iran.

Mr Obama has responded to Israeli concerns by hardening the US position. In March, he said that “all options” were on the table for dealing with Iran’s nuclear ambitions, pointedly adding: “Iran’s leaders should understand that I do not have a policy of containment; I have a policy to prevent Iran from obtaining a nuclear weapon.”

The striking arm of the Israeli air force consists of 125 F-15I and F-16I jets. A war against Iran would require most – perhaps all - of these aircraft to hit targets between 900 and 1,200 miles from their home base. That hinges on air-to-air refuelling; yet, on paper, Israel has only seven KC-707 tanker planes. Would that slender lifeline be enough to get the aerial armada all the way to Iran and back again? Many experts doubt whether this would be possible. Michael Hayden, a retired US air force general and former CIA director, has stated flatly that Israel could not do the job.

Even if all the nuclear facilities could be hit successfully, Israel’s bombs may not be powerful enough to wreck their targets. The heaviest weapon in the Israeli arsenal is the GBU-28 “bunker buster”. But Iran’s uranium enrichment plant at Fordow is dug into a mountainside, protected by about 260 ft of rock and earth. Even this fearsome weapon might not be enough to deal with Fordow.

Work on this installation is believed to be continuing, with the aim of hardening its weak points, notably the entrances and ventilation shafts. If Fordow is already invulnerable to Israeli attack – or soon to become so – Iran would be able to concentrate the materials and expertise for nuclear weapons inside what Ehud Barak has called a “zone of immunity”.

Hence Israel’s pressing sense of urgency. Its decision-makers feel their option for taking action, if it exists, is slipping away. America, however, can still afford to wait. The superpower’s air force could deliver the GBU-57 Massive Ordnance Penetrator, the world’s most powerful conventional bomb, which even Fordow might not be able to resist.

How these sombre calculations will work out is impossible to predict. Supposedly critical moments in the confrontation with Iran have come and gone. Unless things change, however, a genuinely perilous juncture will arrive one day – and it could be closer than we care to think.